Whole Field Microscale Deformation Measurements by Optical and Scanning Electron Microscopy

Shan Huang
Department of Engineering Mechanics
University of Nebraska
Lincoln, NE
M.S. Advisors:  Dr. Wei Tong and Dr. S.I. Chou

Date:  Friday, April 25, 1997
Time:  12:30 p.m.
Place:  306 Bancroft Hall


A novel experimental technique was developed and applied to measure the whole field deformation at the microscale. In-situ mechanical testing experiments were carried out using both optical microscopy (with a field of view of 1 mm x 1 mm) and scanning electron microscopy (with a field of view of 50 mm x 50 mm) as an image formation system of deformed specimen surfaces. The digital image correlation method (DIC) was successfully used to deduce the displacement and strain fields. The DIC technique compared two images before and after the deformation, using Newton-Raphson method to search a small but similar region in both images by a linear 2D deformation mapping. The solution of displacements corresponding to the center of the small region (subset) was obtained by minimization of a certain correlation parameter which measures the best matching between these two images. Repeating the procedure over the entire digital image, whole field displacement data were acquired. The accuracy and reliability of the new technique were evaluated both numerically and experimentally for optical and electron digital images. The developed technique was used in selecting an optimum design of simple shear sheet specimens and has great potential in detecting the shear deformation and failure of small scale Pb-Sn solder joints in microelectronic packaging.